Is a high protein diet bad for the kidneys?

High protein diets (more than 1.5 grams per kilogram of bodyweight per day) and their putative detrimental effects on the kidneys is a controversial topic that has been researched and discussed ad nauseam. However, there is no conclusive answer to this question in people without kidney disease. For instance, a 2018 meta-analysis of small studies including a total of 1,358 healthy adults without kidney disease suggests that following high protein diets (1.8 g protein/kg) for up to 2 years does not worsen kidney function (measured by changes to the glomerular filtration rate GFR) when compared to low protein diets (0.9 g/kg).^[1] This analysis is limited due to lack of randomization and blinding on included studies.

Mechanistically, increased protein intake might cause kidney hyperfiltration (to clear extra nitrogen waste from the ingested proteins). This can lead to inflammation and kidney damage in some people. A few observational studies have found that increased protein intake is associated with decreased kidney function in people who develop hyperfiltration, and in those at risk for developing kidney disease (e.g., those with diabetes). Also, high animal protein intake has been associated with an increased risk of developing chronic kidney disease (CKD).^[2]

In people with existing CKD, it is generally best to avoid high-protein diets to preserve kidney function. In those with moderate to severe CKD, a low protein diet is indicated.^[3] Individualized diets in CKD should be discussed with a medical professional.